Some anti-slip cups on market a present are shown in FIGS. 1-6. The first kind of them shown in FIGS. 1 and 2 has an annular groove A0 in the bottom wall A3 for an annular washer A1 made of hard plastic to fit securely in. The annular washer A1 is provided with three curved grooves A10 for three curved ribs A20 to fit in and extend out of the bottom wall so that the three curved ribs A2 forming an anti-slip ring A2 can prevent a cup from slipping. But the disadvantage of this kind is that combining the annular washer A1 with the cup bottom wall should be performed by a supersonic processing machine, which increases its cost.
The second kind shown in FIGS. 3 and 4 has an annular groove B01 in the cup bottom wall B0 for an annular anti-slip band B1 to fit in and extend out of the bottom wall Bo. Its disadvantage is that the annular anti-slip band B1 is liable to fall off the cup.
The third kind shown in FIGS. 5 and 6 has a projection disc C10 on the cup bottom wall C1, and an annular anti-slip band C0 made of PVC having an inner annular recess fit around the disc C10. Its disadvantage is that the anti-slip band is too high, making the cup insecure because of the high center of gravity of the cup.